1. Technical Field
The present invention relates to a relative position detection device for a vehicle, and in particular to a relative position detection device that is applicable to a travelling system that allows a following vehicle to follow a preceding vehicle, which detects a relative position of the preceding vehicle and the following vehicle in the right and left direction.
2. Related Art
In related art, an unmanned vehicle travelling system is known that includes first and second unmanned vehicles and allows the first and second unmanned vehicles to travel such that the first unmanned vehicle precedes and the second unmanned vehicle follows the first unmanned vehicle.
In this regard, JP-A-H02-076009 discloses an unmanned vehicle travelling system including the first and second unmanned vehicles. In the travelling system, the second unmanned vehicle is provided with a plurality of reflective photoelectric switches on the front surface thereof, and the first unmanned vehicle is provided with a reflecting plate on the rear surface thereof. The photoelectric switches are separated from one another in the right and left direction by a predetermined distance. The reflecting plate is located on the same height as the photoelectric switches.
The photoelectric switches on the second unmanned vehicle emit light toward the first photoelectric switches. Then, only the photoelectric switches that receive the light reflected by the reflecting plate are turned on. Thus, an amount of positional deviation in the right and left direction of the second unmanned vehicle with respect to the first unmanned vehicle can be determined by detecting which photoelectric switches have been turned on.
In a travelling system that allows logistic vehicles or the like to travel in a platoon of vehicles, a distance between a preceding vehicle and a following vehicle increases compared to the travelling system disclosed in JP-A-H02-076009. The long distance between the vehicles makes it difficult to detect an amount of positional deviation in the right and left direction of the following vehicle with respect to the preceding vehicle by using light having a large attenuation factor with respect to a transmission distance, as described in JP-A-H02-076009. Additionally, on daytime public roads, there is a large amount of ambient light (white noise). The also makes it difficult to detect the amount of positional deviation in the right and left direction of the following vehicle with respect to the preceding vehicle by using light.
Further, in the case where ultrasound waves or electromagnetic waves are transmitted from a plurality of sensors separated from one another in the right and left direction by a predetermined distance as disclosed in JP-A-H02-076009, the long distance between two vehicles widens the range in which the ultrasound waves or electromagnetic waves are received. This allows the reflected waves to be received by sensors other than sensors opposed to the reflection plate, thereby reducing detection accuracy of the amount of positional deviation in the right and left direction. From this, a technique disclosed in JP-A-H02-076009 is applied to use narrow-directivity ultrasound waves or electromagnetic waves, but then cannot be used for wide-directivity ultrasound or electromagnetic waves.